The present invention relates to improvements in the use of magnetic resonance imaging, and more particularly to the study of tissue metabolism through the use of oxygen-16.
The ability to produce excellent images of the internal anatomical structure of living beings using nuclear magnetic resonance signals has been well established. Magnetic resonance imaging ("MRI") is highly sensitive to the relaxation times of the nuclei emitting a magnetic resonance signal, and different relaxation times are manifested as different contrasts within the image. The tissues within the various organs and structures of a patient exhibit markedly different relaxation times. Diseased and injured tissue can result in changes in relaxation time relative to healthy tissue. Consequently, MRI produces very high contrast images of anatomical structure, in which injured and diseased tissues are clearly delineated from normal tissue.
Only nuclei containing an odd number of nucleons (protons and neutrons) emit a magnetic resonance signal. While the imaging of oxygen could be useful in the study of tissue metabolism, oxygen-16, the most common isotype of oxygen, has an even number of nucleons and cannot be imaged directly by magnetic resonance imaging. Oxygen-15, which contains an odd number of nucleons, is radioactive and potentially dangerous to the patient. Oxygen-17, which also contains an odd number of nucleons, is not radioactive, but is present in only trace amounts. Enriched oxygen-17 has limited availability and is expensive to prepare. U.S. Pat. No. 5,339,814 to Lasker discloses a process for visualizing tissue metabolism using a gas of an effective imaging amount of oxygen-17. U.S. Pat. No. 4,996,041 to Arai et al. discloses a diagnostic imaging agent including a complex of oxygen-17, a biologically acceptable liquid carrier, such as a perfluorinated compound, and an emulsifying agent. These references do not overcome the disadvantages of the use of oxygen-17.